Frequency Hopping Communication System Research Articles

Intelligent decision-making for a “Three-Variable” frequency-hopping pattern based on OC-CDRL

The frequency hopping pattern of the existing frequency hopping communication system is not designed according to the electromagnetic interference environment, resulting in blind anti-jamming. Therefore, to address this problem, a “three-variable” frequency-hopping pattern is proposed, where the frequency, hopping rate, and instantaneous bandwidth of the frequency-hopping signal vary randomly based on the background electromagnetic interference. The decision-making problem of the “three-variable” frequency-hopping pattern is modeled as a Markov decision process (MDP) by constructing the state-action-reward tuple. The designed frequency varies continuously within a small frequency band selected from a pseudo-random sequence to alleviate the problem of dimension explosion in decision-making. At the same time, discrete values for the hopping rate and instantaneous bandwidth are designed. To solve this MDP problem efficiently, a combined deep reinforcement learning algorithm (OC-CDRL) based on optimistic exploration and conservative estimation is proposed, which combines the features of TD3 and D3QN algorithms and designs the corresponding states, actions, and rewards to deal with continuous and discrete action spaces, respectively. To address the problem that the D3QN algorithm tends to fall into local optimal solutions, an optimistic exploration strategy (OES) for action selection is proposed to improve the degree of exploration. Moreover, the loss function is improved by conservatively estimating state–action pairs outside the experience replay buffer, reducing the overestimation of the optimistic action-value function and increasing the stability and convergence of the algorithm. Comparative simulation results of the algorithms in different electromagnetic interference environments show that the OC-CDRL algorithm effectively avoids most regions with higher interference and has better adaptability and anti-jamming capability.

The Channel Fading Influence of the Receiver Operating Characteristics of the TT&C Receiver Based on the Dual-Sequence Frequency Hopping

Aimed at the antijamming needs of the space tracking, telemetry command (TT&C) receiver under a low signal-to-noise ratio, the anti-interference advantage of the dual-sequence frequency hopping (DSFH) communication system is applied. The channel amplitude fading influence of the receiver operating characteristics (ROC) of the TT&C receiver based on the DSFH is studied. Firstly, based on the typical channel model of the Rayleigh fading without direct path transmission, the conditional Fokker-Planck equation (FPE) is obtained by analyzing the statistical independence of the Rayleigh fading signal and SR output particle moments. Secondly, the probability density function (PDF) of the DSFH signal via channel Rayleigh fading enhanced by stochastic resonance (SR) is obtained by introducing the decision time. Thirdly, the detection probability, false alarm probability, ROC, and system bit error rate (BER) of the DSFH signals enhanced by SR under the Rayleigh fading conditions are obtained, under the minimum BER criterion. Finally, the conclusions are reached: one is that the DSFH signals via channel Rayleigh fading can still be detected by the SR system under low SNR, and the other one is that the SNR can reach the -13 dB by the reception of DSFH signal enhanced by SR, when the Rayleigh fading parameter is 0.2042.

Variable-Speed Frequency-Hopping Signal Sorting: Spectrogram Is Sufficient

In this paper, we present a novel signal sorting method aimed at reducing the impact of interference and noise while achieving blind detection and accurate sorting of a variable-speed frequency-hopping communication system. To achieve this, we combine spectrogram analysis with an innovative sorting approach. First, we generate the spectrogram of the received signal, and then employ a morphology filter to effectively eliminate noise and sweep frequency interference from the spectrogram. Subsequently, we identify and mark connected domains in the spectrogram, from which we extract the duration data to create a dataset specifically for separating fixed-frequency interference. Furthermore, we propose a specialized time alignment algorithm designed to accommodate the unique characteristics of variable-speed frequency-hopping signals, enabling precise sorting of variable-speed frequency-hopping signals. Through rigorous comparative evaluations against existing algorithms, we demonstrate that our proposed approach provides superior accuracy by offering a clearer representation of the time–frequency situation of the received signals. The proposed method provides a high correct sorting probability which is equal to 0.8 when signal-to-noise ratio is 0 dB and reaches 1 when signal-to-noise ratio reaches over 12 dB. In comparison, the correct sorting probability of the comparison algorithm is far inferior to the proposed algorithm.

Intelligent Reception of Frequency Hopping Signals Based on CVDP

The frequency hopping communication systems have been widely used in anti-jamming communication due to their anti-interception and anti-interference capabilities. With the increasingly complex electromagnetic environment, the transmitter of the frequency hopping communication system adopts more flexible frequency hopping patterns to cope with interference. Therefore, to address the problem of traditional frequency hopping receiver systems being unable to receive properly due to intelligent frequency hopping sequence decisions made at the transmitter, we design a CVDP (CNN_VIT_Dual Multi-head Probsparse Self-attention) network based on a convolutional neural network (CNN) module and Transformer Encoder module to realize the intelligent reception of frequency hopping signals. The designed CNN module extracts the global features and spatial information of the time-frequency spectrograms and serves as the input of the VIT (Vision Transformer) network, which not only solves the problem that the VIT network is difficult to converge on small data sets but also improves the stability and robustness of the VIT network. In the Transformer Encoder module of the VIT network, a dual multi-head self-attention mechanism is used to extract critical time-frequency features and a Probsparse self-attention idea is introduced to reduce the computational complexity. Simulation results on hopping frequency estimation and received BER(Bit Error Rate) of CVDP networks in different interference and channel environments show that when a hopping sequence is unknown, CVDP-based intelligent hopping receiver systems can achieve nearly the same receiver performance as conventional reception systems in which a hopping sequence is known.

Deep-Learning-Based Recovery of Frequency-Hopping Sequences for Anti-Jamming Applications

The frequency-hopping communication system has been widely used in anti-jamming communication due to its anti-interception and anti-jamming performance. With the increasingly complex electromagnetic environment, the frequency-hopping communication system needs more flexible frequency-hopping patterns to deal with interferences, which brings great challenges to the communication receiver. In this paper, an intelligent receiving scheme of frequency-hopping sequences is proposed, which combines time–frequency analysis with deep learning to realize an intelligent estimation of frequency-hopping sequences. A hybrid network module is designed by combining a convolutional neural network (CNN) with a gated recurrent unit (GRU). In the proposed network module, the combination of a residual network (ResNet) and squeeze and extraction (SE) improves the feature extraction and expression capabilities of the CNN network. The GRU network is proposed to solve the problem of dealing with signals with variant input lengths. A transfer learning scheme is further proposed to deal with communications systems with different frequency-hopping sets. Simulation results show that the proposed method has strong generalization ability and robustness, and the bit error rate (BER) performance of intelligent receiving is close to the receiving performance under ideal conditions.

Optimal and near-optimal frequency-hopping sequences based on Gaussian period

<abstract><p>Frequency-hopping sequences (FHSs) have a decisive influence on the whole frequency-hopping communication system. The Hamming correlation function plays an important role in evaluating the performance of FHSs. Constructing FHS sets that meet the theoretical bounds is crucial for the research and development of frequency-hopping communication systems. In this paper, three new classes of optimal FHSs based on trace functions are constructed. Two of them are optimal FHSs and the corresponding periodic Hamming autocorrelation value is calculated by using the known Gaussian period. It is shown that the new FHSs are optimal according to the Lempel-Greenberger bound. The third class of FHSs is the near-optimal FHSs.</p></abstract>

Optimal Constructions of Low-Hit-Zone Frequency-Hopping Sequence Sets via Cyclotomy

In complex environments of wireless communication, to improve the communication anti-interference performance, quasi-synchronous frequency-hopping (FH) communication system requires low-hit-zone (LHZ) FH sequence sets with optimal Hamming correlation (HC) properties and flexible parameters. In this paper, based upon cyclotomy theory, two classes of LHZ FH sequence sets with flexible parameters not included in the literatures are designed, and the periodic HC properties of which are analyzed. It turns out that the designed LHZ FH sequence sets are optimal on the maximum periodic HC. And thus the new constructions can be used to provide optimal FH sequence sets for quasi-synchronous FH communication system.

Joint power and hopping rate adaption against follower jammer based on deep reinforcement learning

AbstractAs an effective anti‐jamming approach, frequency‐hopping (FH) technology has been widely applied to tactical communication system, providing reliable communication guarantee and improving resilience against conventional interference under strong confrontation environment. Key challenges for tactical wireless communication network face are the smart follower jammer with responsive spectrum reconnaissance and intelligent decision‐making capabilities. In response, this article investigates a deep reinforcement learning based anti‐jamming scheme, with the aim of maximizing the system throughput. The interactions between a radio transmitter and a smart follower jammer are formulated as a hierarchical anti‐jamming dynamic game model, in which the radio terminal decides transmission power and hopping rate according to the state feedback information, and the jammer chooses spectrum scanning rate accordingly to minimizing the rewards of the FH communication system. We prove that there is a Nash equilibrium (NE) strategy for static and dynamic environment in the game. A double deep Q‐network with prioritized experience reply (PDDQN) based anti‐jamming scheme is proposed to approximating the optimal power control and hopping strategy without being aware of the environment and jamming parameters. Finally, simulation results demonstrate that the proposed algorithm efficiently provide better throughput and jamming resistance.

Time-frequency analysis-based deep interference classification for frequency hopping system

It is known that interference classification plays an important role in protecting the authorized communication system and avoiding its performance degradation in the hostile environment. In this paper, the interference classification problem for the frequency hopping communication system is discussed. Considering the possibility of the presence of multiple interferences in the frequency hopping system, in order to fully extract effective features of the interferences from the received signals, the linear and bilinear transform-based composite time-frequency analysis method is adopted. Then, the time-frequency spectrograms obtained from the time-frequency analysis are constructed as matching pairs and input to the deep neural network for classification. In particular, the Siamese neural network is used as the classifier, where the paired spectrograms are input into the two sub-networks of the deep networks, and these two sub-networks extract the features of the paired spectrograms for interference-type classification. The simulation results confirm that the proposed algorithm can obtain higher classification accuracy than both traditional single time-frequency representation-based approach and the AlexNet transfer learning or convolutional neural network-based methods.

Chinese remainder theorem‐based construction of optimal no‐hit‐zone frequency sequence set with wide gap

In frequency-hopping (FH) communication systems, frequency-hopping sequences (FHSs) determine systems' performance. For the quasi-synchronous FH communication systems, no-hit-zone (NHZ) frequency sequences are good at preventing multi-path interferences. If the two neighbouring frequency components of an FHS have enough gap, the FH communication system's anti-interference ability will be significantly improved. Here, a Chinese remainder theorem-based construction of optimal NHZ-FHS sets with wide gap is proposed.

Efficient Low-Complexity Turbo-Hadamard Code in UAV Anti-Jamming Communications

Unmanned aerial vehicle (UAV) systems undergo a period of rapid development in both civil and military scenarios. A major challenge in the malicious jamming environment is to guarantee the reliability of UAV communications links. Frequency hopping (FH) is one of the most commonly used means of combatting the influence brought about by jamming. In this paper, we integrate low-rate codes into an anti-jamming FH communications system, and propose an efficient and low-complexity turbo-Hadamard code scheme. Tail-biting is applied to design the component convolutional-Hadamard codes, and a corresponding decode algorithm is used for implementation in the UAV hardware platform. Numerical simulation results demonstrate that the anti-jamming performance of this method is improved as compared with conventional concatenated codes. Finally, we compare the complexity and transmission efficiency of the proposed algorithm with the algorithms implemented on the field programmable gate array (FPGA) platform in detail.

Sets of Wide-Gap Frequency-Hopping Sequence With Optimal Maximum Hamming Correlation

In application, frequency-hopping (FH) communication system often suffers various interferences, such as single frequency narrow-band interference, partial band blocking interference and tracking interference, and so on. For all that, by using optimal Wide-Gap (WG) FH sequences, FH communication system can significantly improve the anti-interference performances. In this paper, the relations betweenWG FH sequence theoretic bounds published in the journal IEEE Access (Peihua Li et al., 2019) are first made clear, and then five types of generalized methods are presented to design new classes of WG FH sequence sets. It is shown that all designed WG FH sequence sets are optimal according to the bound derived by Peihua Li et al. And by selecting appropriate original sequence sets, many of the optimal WG FH sequence sets can be obtained by our methods. Most importantly, these WG FH sequence sets have new parameters that are not covered in the literature.

Constructions of Optimal Uniform Wide-Gap Frequency-Hopping Sequences

In frequency hopping (FH) communication systems, frequency hopping sequences (FHSs) are crucial in determining the system’s anti-jamming performance. If FHSs can ensure a wide-gap between two adjacent frequency points to avoid the frequency points with high interference probability, it will significantly improve the FH communication system’s anti-interference ability. Moreover, if each frequency point appears at the same number of times in a sequence period, the system’s anti-electromagnetic interference will be enhanced. Therefore, it is desirable to employ FHSs with low Hamming autocorrelation, wide frequency-hopping gap, and good uniformity in practical applications. However, to the best of our knowledge, no such infinite classes of FHSs have been reported in the literature to date. This paper aims to present two constructions of uniform wide-gap frequency-hopping sequences (WGFHSs) by concatenating two or three adequately designed sequences. For the first time, we obtain two infinite classes of WGFHSs, which are optimal with respect to the well-known Lempel-Greenberger bound.

An Innovative FPGA Implementations of the Secure Frequency Hopping Communication System Based on the Improved ZUC Algorithm

Frequency Hopping (FH) is a significant anti-interception and anti-interference, so some wireless communication systems extensively use it. Then it can offer better security performance of the system via combining cryptographic algorithms with FH. This paper presents a detailed theoretical design and hardware implementation of an evolutionary ZUC stream cipher algorithm on FPGA. Using some encryption algorithms can improve the security of the FH system by increasing its complexity, including SNOW3g, ZUC algorithm, Chaos system, and other cipher methods. ZUC (named for Zu Chongzhi, a famous mathematician in ancient China) is bitstream encryption that builds the core of the 3GPP integrity algorithm 128-EIA3 and the 3GPP confidentiality algorithm 128-EEA3, providing authentic security services in 4G, even in 5G (IMT-2020) to some extent. The article presented an evolutionary three-layers structure of the ZUC FH system, which innovatively applied the permutation polynomial algorithm and an evolutionary DES cipher algorithm. The introduction of that new DES and the permutation polynomial can efficiently increase the security performance of the ZUC system but also avoid some shortcomings of the UHF (Ultra High Frequency) communication. The experiment of this research designed software by coding VHDL language and implemented hardware using a XILINX Virtex-5 FPGA. The finished experiment gave, analyzed, and compared all results according to the performance of the proposed system and hardware resources. The tests for evaluating the randomness and security denote that the constructed sequences have better performance, including the randomness, linear complexity, and hamming correlations, and pass the NIST test finally. The experimental results show that this improved ZUC cipher stream algorithm proposed in the article can provide a high throughput of 2.08 Gbps under a 65MHz clock frequency. The authors will focus their future work on applying the evolutionary S-box and the algorithm with better security performance.

Optimal no‐hit‐zone frequency hopping sequence sets with wide gap

Using no-hit-zone frequency-hopping (FH) sequences with wide gap (WG NHZ FH sequences), the quasi-synchronous (QS) FH communication systems not only have good capability of preventing muti-path interference but also have strong capabilities of resisting the enemy's intentional interferences in the complicated electromagnetic interference conditions. This paper designs a new class of optimal WG NHZ FH sequence set which was not presented previously. It significantly meet the needs of high reliable QS FH communication under complicated electromagnetic interference conditions.

Miniaturization of Frequency-Reconfigurable Antenna Using Periodic Slow-Wave Structure

A challenge for frequency-reconfigurable antennas is how to realize miniaturized structures while preserving satisfying radiation performance in whole operation bandwidth. To address this problem, we apply planar periodic slow-wave structure (PSWS) with controlled dispersion features for miniaturization of antenna. Due to the subwavelength property and large propagation constant, this design holds a much more compact size than conventional microstrip structures. The proposed antenna consists of a double-layered dielectric substrate with the tunable patch on the top and a bias network combining with the feeding part on the bottom. The operating frequency is electronically controlled by the varactors shortened to the ground on nonradiating edges. It ranges from 4.87 to 5.52 GHz when the bias voltage varies from 9 to 16 V. Both simulated and measured results show that the proposed antenna maintains acceptable gains and similar radiation patterns while shrinking the size effectively. The proposed miniaturized and frequency-reconfigurable antenna holds potential applications in the ultracompact frequency hopping communication systems.

A New Frequency Hopping Signal Detection of Civil UAV Based on Improved K-Means Clustering Algorithm

The rapid development of civil UAV promotes the social and economic development, and the frequent “flying illegally” events has brought great challenges to aviation safety and government supervision. The frequency hopping communication system used in UAV data transmission and control link has the advantages of anti-jamming and anti-interception, and its complex electromagnetic environment, which also brings great difficulties to UAV detection. In this paper, the detection of civil UAV is realized by frequency hopping signal monitoring. Firstly, by analyzing the signal characteristics of UAVs, an adaptive noise threshold calculation method is proposed for find the signals from spectrum data. Then, the improved clustering analysis algorithm is proposed based on constructed the waveform shape characteristics and peak characteristics of UAV frequency hopping signal. Finally, according to the designed experimental process, the experimental environment is set up, and the UAV monitoring, discovery and parameter estimation are realized by using the improved clustering analysis algorithm, and compared with K-means, K-means++, DBSCAN, Multi-hop and Auto-correlation methods. The results show that the method has certain robustness and has a good application prospect.

Signal Sorting Algorithm of Hybrid Frequency Hopping Network Station Based on Neural Network

In a non-cooperative frequency hopping communication system, the frequency hopping network station sorting of the received hybrid signals plays an important role and becomes an active research area in recent years. In order to solve the problem that the currently widely used clustering algorithm can not achieve satisfactory accuracy. In this paper, we propose a signal sorting method for hybrid frequency hopping network stations by applying the neural network to classify the frequency hopping description words of signals. Additionally, the conjugate gradient algorithm is utilized in the neural network training process to improve the convergence speed. Simulation results demonstrate that when compared with the clustering algorithm, the proposed algorithm converges with fewer iterations and delivers better sorting accuracy, especially in a low signal to noise ratio environment.

Signal Sorting Algorithm of Hybrid Frequency Hopping Network Station Based on Neural Network

In non-cooperative frequency hopping communication system, the frequency hopping network station sorting of the received hybrid signals plays an important role and becomes an active research area in recent years. In order to solve the problem that the currently widely used clustering algorithm cannot achieve satisfactory accuracy. In this paper, we propose a signal sorting method for hybrid frequency hopping network stations by applying the neural network to classify the frequency hopping description words of signals. Additionally, the conjugate gradient algorithm is utilized in the neural network training process to improve the convergence speed. Once the neural network training is finished, only one frequency hopping description word of the input signal is required to obtain its own network station label in real time. Simulation results demonstrate that when compared with the clustering algorithm, the proposed algorithm converges with less iterations and delivers better sorting accuracy, especially in a low signal to noise ratio environment.

Binary-Sequence Frequency Hopping Communication Method Based on Pseudo-Random Linear Frequency Modulation

To improve the signal detection performance of binary-sequence frequency hopping communication when the complementary channel is jammed, a binary-sequence frequency hopping communication system based on pseudo-random liner frequency modulation (LFM) is proposed. The transmitting end uses the chirp signal to carry out the in-band spread spectrum of the binary-sequence frequency hopping signal, and then sends it out through the radio frequency front end. At the receiving end, the received signal is dehopped and processed by fractional Fourier transform. The source information is obtained by sampling decision. Firstly, a binary-sequence frequency hopping system model based on pseudo-random LFM is constructed. Secondly, the bit error rate expression of anti-partial band jamming and follower jamming under the Rice channel is derived. The results show that this method has at least 5 dB performance gain than binary sequence frequency hopping for different parameter settings under partial band jamming and follower jamming, and the anti-jamming performance is significantly better than the conventional frequency hopping communication.